In tire uniformity machines, a tire is tested by rotating it at various speeds to ensure that the tire has been constructed to perform within quality control standards. During this testing process, the tire is rotated, and the tire uniformity machine examines the tire's integrity, shape, and surface qualities to a high degree of accuracy. At times, during examination, the tire uniformity machine detects irregularities in the tire. Any irregularity in the integrity, surface, and shape of the tire may be corrected by removing material from appropriate portions of the tire.
To remove material from a tire, known tire uniformity machines typically employ a grinder having a single grindstone rotating in relation to the rotation of the tire. In known grinders, the grindstone is cylindrical, and the application of the grindstone occurs in a rotary fashion. Often a motor and gear box arrangement is used to control the speed and direction of rotation of the grindstone. As such, the motor is connected to the gear box arrangement by belts or chains and a series of pulleys or sprockets. Because the motor needed to drive the belts or chains, and the gear box arrangement is bulky, the housing of the motor projects to such an extent that the confines of the tire uniformity machine prevent the grindstone from being actuated in a linear fashion inward and outward with respect to the tire. As such, to accommodate the limited area for positioning the grinder, known tire uniformity machines attach the motor distally from the grinder on the pivoting arm, away from the confines of the tire uniformity machine, so that rotation of the pivoting arm will position the grindstone adjacent the tire.
Rotation of the pivotal arm, however, may not aim the grindstone directly at the center of the tire. That is, the center line and the contact point of the grindstone travel in an arc in an attempt to tangentially contact the tire.
To better position the grindstone to remove material from the tire, known grinders pivotably support the grindstone relative to the pivoting arm. As such, the position of the grindstone can be pivoted to account for the indirect aim of the pivoting arm. To provide such pivotal movement, known grinders incorporate a series of linkages. In some cases, as many as five linkages may be used. Due to machining tolerances, each link is a potential source of error. When multiple links are used, such errors are compounded making it more significant in terms of accurately positioning the grindstone to remove material from the tire.
In fact, when dual grindstones, a leading and a trailing grindstone, are provided, use of such linkages virtually eliminates the ability of the grinder to have both grindstones strike the tire simultaneously, and, in some cases, may cause one of the grindstones to be out of contact with the tire. The trailing grindstone is often used in an attempt to correct irregularities created by the first grindstone. However, when errors occur using the linkages, the leading or trailing grindstone is precluded from performing its corrective function.
As discussed above, the pivoting arm supporting single or dual grindstones can be a source of inaccuracy in positioning the grindstone or grindstones relative to the tire. Moreover, pivotably supporting the grindstone relative to the pivoting arm so that the grindstone or grindstones can be pivoted to account for rotation of the pivoting arm introduces additional inaccuracies. As such, there is a need for a grinder having single or dual grindstones repositionable with respect to a tire without using various linkages which can introduce inaccuracies during positioning. Such a grinder should be capable of initiating good, accurate contact of its grindstone or grindstones with the tire in a repeatable manner.
Existing tire uniformity machines make spot corrections by grinding selected portions of a tire for brief periods of time. To that end, shoulder grinders are used to contact the sidewalls of the tire, and a center grinder contacts the tread portion to grind off any imperfections detected during the testing process. The shoulder and center grinders are generally held in fixed vertical and angular positions and driven inward to contact the tire. In that regard, grinding is performed statically and movement of the grindstone while it is grinding is not contemplated. It is desirable to have a tire uniformity machine having a dynamic grinding assembly capable of automatically positioning the grindstone. It is further desirable to provide a grinding assembly capable of grinding a tire according to a selected profile.